1. Field of the Invention
The present invention relates to an image stabilizer for correcting an image blur due to hand-held shooting, and an optical instrument therewith.
2. Description Related to the Prior Art
Many optical instruments including digital still cameras have an image stabilizer or a shake correction device for correcting an image blur caused by vibration or a camera shake due to hand-held shooting. The image stabilizer is constituted of a shake detector for detecting the camera shake, a holder for movably holding an optical element such as a taking lens or an image sensor, a computing unit, an actuator for shifting the holder in a plane where the optical element is orthogonal to a photography optical axis, and a position detector for detecting the position of the optical element. The computing unit calculates which direction and how much the optical element should be shifted, based on a detection result of the shake detector such as an angular velocity sensor. The actuator e.g. a motor performs feedback control of the shift of the optical element during the camera shake, by using a calculated shift amount as a target value and a detection value of the position detector as a measurement value.
Some image stabilizers use a flexible printed circuit (hereinafter abbreviated as FPC) for connecting the actuator to its control circuit. In KATO et al. (U.S. Pat. No. 5,680,251), for example, a lens barrel incorporates gears and a motor for moving a shake correction lens. An FPC for connecting the motor to a control circuit is disposed in a small space between the gears and an inner wall of the lens barrel. According to SAKAMOTO et al. (Japanese Patent Laid-Open Publication No. 2006-030749), an image stabilizer is provided with a coil being a part of an actuator, and an FPC connects the coil to its control circuit. The FPC is bent in the shape of an arc the center of which coincides with a photography optical axis, so as not to interfere with shift of a shake correction lens.
All of MAEDA et al. (Japanese Patent Laid-Open Publication No. 2007-058089), STAVELY et al. (United States Patent Application Publication No. 2006/0017815) and HIROTA et al. (U.S. Pat. No. 7,576,778) disclose the type of image stabilizer in which an image sensor is shifted in a plane orthogonal to a photography optical axis. According to MAEDA et al., an FPC connected to an image sensor is bent in an arc shape along an outer surface of an image sensor holder to allow shift of the image sensor. In STAVELY et al., an image sensor is mounted on a printed circuit board that is movable along a photography optical axis and in directions orthogonal to the photography optical axis. The printed circuit board is coupled to approximately arc-shaped FPCs. The FPCs allow shift of the printed circuit board in directions orthogonal to the photography optical axis, while preventing rotation of the printed circuit board about the photography optical axis. In HIROTA et al., an FPC for connecting an image sensor to a control circuit board is sagged to allow shift of the image sensor in directions orthogonal to a photography optical axis.
KATO et al. is not applicable to the type of image stabilizer with a shiftable image sensor because the FPC is disposed in the small space in the lens barrel to save space. SAKAMOTO et al., MAEDA et al., STAVELY et al. and HIROTA et al. are applicable to an image stabilizer with a shiftable image sensor because the FPC is sagged, but still have problems caused by the sag of the FPC, that is, reaction force of the sag and variations in bending shape.
The reaction force occurs when an FPC has been bent with shift of an image sensor. Since the reaction force applies a load to an actuator, it is preferable to minimize the reaction force as much as possible. To reduce the reaction force, it is conceivable to elongate a sag. The long sag, however, requires a large storage space. The short sag, on the other hand, causes the large reaction force, and requires a high-power actuator, resulting in increase in size and cost of an image stabilizer.
A sagged shape is formed in an FPC manually or with a jig, and has wide variations in size and shape. Accordingly, it is difficult to precisely estimate the sagged shape of the FPC upon shift of an image sensor. To keep the FPC from contact with another component, an FPC receiving chamber has to have a large margin. This was an impediment to downsizing of a digital still camera.